Integrated focusing emitter

ABSTRACT

A method for creating an electron lens includes the steps of applying a polymer layer on an emitter surface of an electron emitter and then curing the polymer layer to reduce volatile content.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to the fabrication of lens designfor electron emitters, particularly those electron emitters used in massstorage and display devices often incorporated in many electronicdevices.

[0002] Computing technology continues to become less expensive whileproviding more capability. To allow computing technology to continuethese positive trends, peripheral devices such as mass storage devicesand display devices must continue to advance. Much criticism has beenvoiced in the trade press about the lack of mass storage devices such asdisk drives, CD-ROMs, and DVD drives, to name a few, to increase theirdata rates up with the advancing speed of the microprocessors found incontemporary personal computers. However, hard disk drives, for examplehave been able to increase their storage density tremendously over thelast decade but are now encountering physical limitations that preventsfurther progress in this area. Display devices, such as LCD monitorshave had difficulty in fulfilling demand due to the complexity ofmanufacturing them with near-zero defects. Further, the use of passiveLCD technology has required the addition of backlights to allow forviewing in different ambient light conditions thereby adding cost andincreasing power requirements.

[0003] Electron beam technology has been present for many years inconsumer products such as television (TV) tubes and computer monitors.These devices use what is known as “hot cathode” electrodes to create asource of electrons that are directed to and focused on the viewingscreen. While research has taken place in a number of new technologicalfields with emission devices, the field of “cold cathode” electronemitters such as Spindt-tips and flat emitters has attracted theattention of many manufacturers.

[0004] Several problems exist in converting this cold cathode technologyto products. One such problem is the creation of an electron focusingstructure that can be used in multiple applications that require a highdensity of cold cathode emitting devices such as with mass storage anddisplay devices. Conventionally, dielectric materials are used as spacermaterial between the electron focusing structure and the electronemitter. However, the cost and complexity of building the electronfocusing structure with dielectric material hinders the rapiddevelopment of new products using cold cathode technology. In order tofurther the introduction of new products using cold cathode technology,more cost effective and simpler processes for building electron focusingstructures and ultimately the mass storage and display devices areneeded.

SUMMARY OF THE INVENTION

[0005] A method for creating an electron lens includes the steps ofapplying a polymer layer on an emitter surface of an electron emitterand then curing the polymer layer to reduce volatile content.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The invention is better understood with reference to thefollowing drawings. The elements of the drawings are not necessarily toscale relative to each other. Rather, emphasis has instead been placedupon clearly illustrating the invention. Furthermore, like referencenumerals designate corresponding similar parts, though not necessarilyidentical, through the several views.

[0007]FIG. 1A is a top view of an exemplary embodiment of an integratedfocusing emitter.

[0008]FIG. 1B is a cross-sectional view of the exemplary embodimentillustrated in FIG. 1A.

[0009]FIG. 2 is an exemplary cross-sectional view of an alternativeembodiment of an integrated focusing emitter with a direct tunnelingemitter.

[0010]FIG. 3 is a perspective view of an exemplary embodiment of adisplay device that incorporates the invention.

[0011]FIG. 4 is a cross-sectional view of an alternative exemplaryembodiment of a display device that incorporates the invention.

[0012]FIG. 5 is a perspective view of an exemplary embodiment of a massstorage device that incorporates the invention.

[0013]FIG. 6 is a cross-sectional view of an alternative exemplaryembodiment of a mass storage device that incorporates the invention.

[0014]FIG. 7 is a block diagram of an exemplary process used to createan integrated focusing emitter including the steps to create an electronlens that incorporates a polymer spacer layer.

[0015]FIGS. 8-14 are illustrations of exemplary process steps to createan electron emitter that provides a base for the electron lens of theinvention.

[0016]FIGS. 15-16 are charts that illustrate exemplary temperatureprofiles for alternative annealing processes used to create an electronemitter.

[0017]FIG. 17 is an illustration of the application of a polymer layerto the electron emitter base.

[0018]FIG. 18 is a chart of an exemplary curing process used to extractvolatile content from the polymer layer shown in FIG. 17.

[0019]FIG. 19 is an illustration of the deposition of a conductive layeron the polymer layer.

[0020]FIG. 20 is an illustration of the masking and etching of theconductive layer of FIG. 19 to create an electron lens opening.

[0021]FIG. 21 is an illustration of the result of a selective etchingprocess that etches the polymer layer to expose the electron emittersurface.

[0022]FIG. 22 is an illustration of the result of a deposition of aemitter cathode layer to finish creating the integrated focusingemitter.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATIVE EMBODIMENTS

[0023] To reduce costs and allow for reduced processing steps, theinvention incorporates using a polymer layer as spacer material betweenthe electron emitter and the focusing lens thereby creating anintegrated focusing lens. To allow for incorporation of a polymer spacerlayer several problems must be overcome.

[0024] First, polymer material generally has volatile components thatcan outgas over time. This outgassing can be a concern when the electronemitter is operating in a vacuum, typically less than 10⁻⁵ Torr of airpressure. The outgassing of polymer material can affect the air pressurelevel, thus requiring an active vacuum pump or getter material to removethe release volatile contents. Further, if the volatile contents of thepolymer are released into the vacuum during operation, an emittedelectron can strike a portion of the volatile content and ionize it. Ifthere is a large voltage potential between components in the devicesincorporating the electron emitter, the ionized volatile componentaccelerates toward the cathode of the emitter and collides with it,thereby causing damage. Thus, it is customary to use spacer materialthat does not outgas. The invention includes a curing process for thepolymer material that reduces significantly the volatile contents of thepolymer material such that a vacuum of less than 10⁻⁵ Torr can bemaintained without active vacuum pumping.

[0025] Second, because of the material interface characteristics, highstress interfaces can exist between a polymer spacer material and theconductive material used to create the electron lens. A high stressinterface can result in rough surfaces and cracks in the conductivematerial that might affect the performance of the electron lens. Theinvention includes using preferably a substantially gold material forthe conductive layer used for the electron lens.

[0026] Third, because the polymer material is etched by using theopening in the conductive layer for the electron lens as a mask foretching polymer material, the etching process preferably accounts for anetch profile with minimal undercutting under the conductive layer thatis used for the electron lens. Too much undercutting causes theconductive layer to not have adequate support and might cause theelectron lens to become deformed and not operate properly.

[0027] Fourth, the etching process for the polymer material must notsignificantly etch the conductive layer used for the electron lens orleave residue from the etching process on the emitter surface. Anymaterial on the emitter surface, such as traces of the conductive lenslayer or polymer material can affect the performance of the electronemitter by changing its emission characteristics.

[0028] Fifth and most important, the etch selectivity of the polymeretch process is important so as to not significantly etch the emittersurface which can damage the electron emitter. Thus, the etch process ofthe invention balances the etch conditions to trade off etch rate, etchresidue, etch selectivity of the conductive lens layer, etch selectivityof the emitter surface, and etching power used. By choosing the properparameters, an etch selectivity between the polymer and the emittersurface greater than 1000:1 is achieved.

[0029] More aspects of the invention will become apparent in thefollowing description of preferred and alternative embodiments of theinvention. The semiconductor devices of the present invention areapplicable to a broad range of semiconductor device technologies and canbe fabricated from a variety of semiconductor materials.

[0030] The following description discusses several presently preferredembodiments of the semiconductor devices of the present invention aspreferably implemented in silicon substrates, since the majority ofcurrently available semiconductor devices are fabricated in siliconsubstrates and the most commonly encountered applications of the presentinvention will involve silicon substrates. Nevertheless, the presentinvention may also advantageously be employed in gallium arsenide,germanium, and other semiconductor materials. Accordingly, the presentinvention is not intended to be limited to those devices fabricated insilicon semiconductor materials, but will include those devicesfabricated in one or more of the available semiconductor materials andtechnologies available to those skilled in the art, for example,thin-film-transistor (TFT) technology using polysilicon on glasssubstrates.

[0031] It should be noted that the drawings are not true to scale.Further, various parts of the active elements have not been drawn toscale. Certain dimensions have been exaggerated in relation to otherdimensions in order to provide a clearer illustration and understandingof the present invention.

[0032] In addition, although the embodiments illustrated herein areshown in two-dimensional views with various regions having depth andwidth, it should be clearly understood that these regions areillustrations of only a portion of a device that is actually athree-dimensional structure. Accordingly, these regions will have threedimensions, including length, width, and depth, when fabricated on anactual device. Moreover, while the present invention is illustrated bypreferred and alternative embodiments directed to active and electronicdevices, it is not intended that these illustration be a limitation onthe scope or applicability of the present invention. It is not intendedthat the active and electronic devices of the present invention belimited to the physical structures illustrated. These structures areincluded to demonstrate the utility and application of the presentinvention to presently preferred and alternative embodiments.

[0033]FIG. 1A is a top view of an exemplary embodiment of the inventionthat integrates an electron lens and preferably, but optionally, anelectrostatic shield, with an electron emitter. In FIG. 1A, the electronemitter 20 emits electrons that are focused using a co-planer electronlens 16 having a lens opening 18. The co-planer lens 16 is formed on aconductive layer and is held at a voltage potential relative to acathode surface of the electron emitter 20. The amount of voltagechosen, lens geometry, and distance from the electron emitter 20determines the amount of focus performed by the co-planer electron lens16. Optionally, on the same conductive layer as the co-planer lens 16 isa co-planer shield 14 that is held at a different voltage than theco-planer lens 16. Preferably, the voltage of the co-planer shield 14 isheld at about the same voltage as an anode target for the electron beamemitted by the electron emitter 20. The co-planer lens 16 is separatedfrom the co-planer shield 14 by a gap 22 to provide electricalisolation.

[0034]FIG. 1B includes a cross-sectional view of the focused emitter ofFIG. 1A along the I-I section. Also included is an anode 76 that is thetarget of the electron beam from electron emitter 20. The electronemitter 20 can be one of several types such as a direct tunnelingemitter, a metal-insulator-metal emitter, ametal-insulator-semiconductor emitter, an array of spindt tip emitters,or a single spindt-tip emitter to name a few. The electron emitter 20 isformed within and/or disposed on a substrate 10, preferably a siliconsubstrate but other substrates such as glass, germanium, or galliumarsenide, for example can be used instead and still meet the spirit andscope of the invention. Disposed on the substrate 10 is a polymer layer12 used as a spacer for the co-planer lens 16 and co-planer shield 14formed in a conductive layer. The electrons emitted by the electronemitter 20 are focused by an electric field formed within the lensopening 18 and are attracted to the anode 76 that is preferably held ata high positive voltage relative to the electron emitter 20. The anode76 is disposed an anode-lens distance 24 to achieve a focused spot onthe anode. If the lens design chosen is such that the anode-lensdistance 24 requires a small distance thereby creating a largeelectrostatic attractive force 26, then the co-planer shield layer 14 isoptionally used and held at about the same potential as the anode 76 toreduce the electrostatic force 26. If the anode 76 is held at aanode-lens distance 24 such that the electrostatic force 26 is weakenough for a given application, then co-planer shield 14 is notnecessary.

[0035]FIG. 2 is an illustration of an exemplary direct tunneling emitterthat incorporates an integrated electron lens of the invention to createan integrated focusing emitter 60. In this embodiment, the substrate 10is preferably a silicon substrate preferably heavily doped. Substrate 10is alternatively any other conductive material or substrate thatprovides a supply of electrons. On substrate 10 a stack of thin-filmlayers 38 is applied or processed to create the direct tunnelingemitter. A tunneling layer 30 is disposed on the substrate 10 and ispreferably less than 500 Angstroms, more preferably about 100 Angstroms.On the tunneling layer is disposed a cathode layer 36 of preferably athin film of metal such as about 50 to about 100 Angstroms of platinum,although other metals can be used. For example, other metals include butare not limited to gold, iridium, molybdenum, chromium, and tungsten. Onthe stack of thin-film layers 38 is disposed a polymer layer 12 used tospace the electron lens 28 from the electron emitter. Preferably, thepolymer layer is between about 2 to about 12 micrometers thick orgreater. An anode 76 is disposed at a anode-lens spacing 24. Theelectron lens 28 is held at a voltage potential relative to the cathodelayer 36 and creates an electric field 34, which focuses the electronsemitted from the electron emitter to create a focused beam 32. Theelectric field 34, the lens opening, and the anode-lens spacing 24 arechosen to provide a desired spot size on the anode 76.

[0036]FIG. 3 is a partial view of an embodiment of an exemplary displaydevice 70 that incorporates the invention. A cathode layer 78 haselectron emitters 20 disposed or formed within that create an electronbeam 50. Disposed on the cathode layer is a polymer layer 12 thatfurther has a lens layer 40 disposed on it. Formed within the lens layer40 and the polymer layer 12 are opening 42 that allow the electron beams50 to exit and reach pixels 72 on the anode 76, preferably the displayscreen. The pixels are preferably made up with phosphor material, eitherin a monochromatic or multiple color order, such as red, green, blue.When the electron beam 50 reaches the pixels 72, the phosphor materialis excited by the electrons and emits photons that create visible light.

[0037]FIG. 4 is an alternative embodiment of an integrated displaydevice 80 that is illustrated in cross-section form. The integrateddisplay device 80 has a substrate 10, preferably a silicon substratethat is processed with semiconductor processing to include a stack ofthin-film layers 38 that incorporate electron emitters 20. The electronemitters 20 create electron beams 50 which are used to excite displaypixel 84 made of phosphorous material. Disposed on the stack ofthin-film layers 38 is a polymer layer 12 that has openings to allowelectron beams 50 to pass through to lens layer 40 disposed on thepolymer layer 12. The lens layer 40 has openings for focusing theelectron beam 50 onto the display pixel 84. The display pixel 84 isformed within anode 86 that captures any stray electrons. The displaypixels 84 and anode 86 are disposed on the display screen 82, preferablya glass or other transparent substrate. The anode 86 is spaced from thelens layer 40 by a spacer 88 that is also preferably a hermetic seal.Optionally, an alternative seal 86 is placed around the display tofurther provide a hermetic seal or adhesive joint between the displayscreen 82 and the substrate 10 with its stack of thin-film layers 38 andpolymer layer 12.

[0038]FIG. 5 is a partial view of an exemplary embodiment of a massstorage device 90 that incorporates the invention. In this embodiment,the mass storage device 90 has at least three substrates, a substrate10, a rotor substrate 92, and a stator substrate 94. The substrate 10has a stack of thin-film layers processed on it that contains activedevices such as electron emitters 20. Disposed on the stack of thin-filmlayers 38 is a polymer layer 12 that provides spacing for electron lens28. The electron lens 28 creates a focused beam 32 that is used toread/write information on the surface of media 96 on the rotor substrate92. The media surface is preferably made up of a phase change materialthat can exist in either a crystalline or amorphous state depending onthe time and amount of energy expended on it by the focused electronbeam. When a low power electron beam is used to read the crystalline oramorphous state, electrons are detected in the rotor substrate 92 by areader circuit 98. The reader circuit 98 includes an amplifier 95 thatdetects the current in the rotor substrate 92 between media contact 91and substrate contact 97. When the focused beam 32 strikes an amorphousspot 93 the amount of current which flows to the amplifier circuit isdifferent than when the focused beam 32 strikes a crystalline area.Preferably, a conventional digital media recording format is used torecord information in the media 96. To make an amorphous spot, ahigh-energy focused beam is presented to the surface of the media 96 fora short time and allowed to cool rapidly. To remove the amorphous spotand return the media 96 to a crystalline state, the amorphous spot 93 isheated with a high-energy focused beam 32 and allowed to cool slowly byslowly changing the energy of the focused beam 32.

[0039]FIG. 6 is an exemplary integrated mass storage device 100 thatincorporates the invention illustrated in cross-sectional form. Asubstrate 10 has a stack of thin-film layers 38 that incorporates theelectron emitters 20. Disposed on the stack of thin-film layers 38 is apolymer layer 12. Disposed on the polymer layer 12 is an electron lenslayer 28 used to focus electrons from electron emitters 20 into afocused beam 32. The substrate 10 and its stack of thin-film layers 32and polymer layer 12 are attached to a rotor substrate 92 using a spacer88 and seal 89 to provide an evacuated environment, preferably less than10⁻⁵ Torr. The rotor substrate 92 has a movable portion containing media96. The movable portion is attached to the rotor substrate 92 usingsprings 152, preferable formed and etched from rotor substrate 92 usingmicro-mechanical machining techniques. The rotor substrate 92 isattached to a stator substrate 94 by seal/adhesive 158. Electricalcontact is made by inter-substrate contacts 156. The stator substrate 94and the rotor substrate 92 control the movement of the movable portionof the rotor substrate 92 by the use of an electrostatic stepper motor154. The electrostatic stepper motor 154 is preferably movable in afirst and second direction but some embodiments may limit the movementto a single direction. By providing for movement of the media 96, eachelectron emitter 20 can read/write several locations on media 96, thusproviding for increased density of information storage. The polymerlayer 12 provides for separation of the electron lens layer 28 from theelectron emitter 20.

[0040]FIG. 7 is a flowchart of an exemplary general process used tocreate an integrated focusing emitter including the steps to create anelectron lens using a polymer spacer layer. These process steps can beimplemented with several different technologies for creating anintegrated focusing emitter using conventional semiconductor processingtechniques known to those skilled in the art. The integrated focusingemitter begins with the selection of a substrate, preferably silicon butother substrates are known to those skilled in the art and can besubstituted and still meet the spirit and scope of the invention. Thepurpose of the substrate is to provide a source of electrons and also toprovide a stable platform for further processing of a stack of thin-filmlayers that contain the electron emitter and also the processing of theintegrated electron lens.

[0041] In step 102, an isolation layer is created on the substrate withat least one opening to define the location of the electron emitter suchas by masking and growing or depositing dielectric materials. For asilicon substrate, the isolation layer is preferably field oxide growth(FOX) or other dielectrics such as thermal oxide, silicon nitride,silicon dioxide, or silicon carbide to name a few. In optional step 104,depending on the isolation layer used, an adhesive layer such astantalum can be placed (disposed) on the isolation layer to allow forbetter adhesion of a first conductive layer that is applied in step 106.In step 108, the first conductive layer is patterned, preferably withphotoresist, to create an opening for the well of the electron emitter.In step 110, the first conductive layer is etched in the opening,preferably a wet etch to create an anisotropic profile although otheretch techniques can be substituted such as a dry etch. In step 112, theadhesive layer is preferably dry etched to create an isotropic profile.The etching of the adhesive layer is not performed of course if theoptional adhesive layer is not used or applied in step 104. In step 116,a tunneling layer is preferably deposited on the exposed substratesurface and on top of the pattern material used to create the opening inthe first conductive and adhesive layers. In step 118, preferably a liftoff process is used to remove the pattern material and to lift off thetunneling material that was disposed on the patterning material withoutremoving the tunneling material that is disposed on the substrate. Forpositive photoresist, the preferable lift off process uses an oxygen ashetch process.

[0042] In step 120 the processed substrate is subjected to an annealingprocess that increases the emission current density of the electronemitter.

[0043] In step 122, the polymer layer is deposited on the processedsubstrate. Then is step 124, the process substrate with the polymerlayer is conditioned by curing the polymer layer to remove volatilecomponents and compounds from the polymer material. The actual curingprocess used will depend on the type of polymer material chosen. In step126, a second conductive layer is deposited on the polymer layer for usein creating the electron lens and optional shield.

[0044] In step 128 the second conductive layer is masked and patternedto create the focusing lens. In step 130, the second conductive layer isetched within the pattern openings to create the lens opening. Then instep 132, a selective etch is performed on the polymer layer to thesurface of the electron emitter with preferably little undercut underthe electron lens. In step 134, a third conductive layer is depositedover the second conductive layer and within the lens opening on thesurface of the electron emitter to create a cathode layer on thetunneling layer of the electron emitter.

[0045]FIGS. 8-22 are exemplary illustrations of the processing of asubstrate 10, preferably a silicon substrate, to create an integratedelectron emitter using specific embodiments of semiconductor processingsteps. The process steps shown are by way of example to make clearer anunderstanding of the invention in a specific embodiment and are notmeant to limit the methods of making the invention.

[0046]FIG. 8 shows substrate 10 having a FOX-mask 44 patterned thereonto define a location for the electron emitter surface. Preferably theFox-mask 44 is a hard mask such as a dielectric but also could be aphotoresist.

[0047]FIG. 9 shows the growth of the field oxide and the removal of theFOX-mask 44 from FIG. 8. The field oxide thickness is typically withinthe range of 3000-10,000 Angstroms.

[0048]FIG. 10 shows the application of an optional adhesive layer 48,preferably tantalum, on the FOX and emitter surface areas over thesurface of the substrate 10. Preferably the adhesive layer 48 is appliedusing a deposition process to a thickness of about 500 Angstroms.

[0049]FIG. 11 shows the application of a first metal layer 52,preferably gold on top of the adhesive layer 48. The preferred thicknessof the first metal layer 52 is about 2000 Angstroms. If a first metallayer 52 is chosen that has good adhesion properties to the insulatinglayer chosen then the adhesive layer 48 is not required.

[0050]FIG. 12 illustrates the results of etching of the first metallayer 52 and the adhesive layer 48. To perform the etching, first afirst metal photoresist is applied on the first metal layer 52 andpatterned to define an opening where etching is to occur. The opening inthe first metal photomask is preferably aligned over the emitter surfacedefined in the FOX material. The first conductive layer is preferablywet etched to form an anisotropic profile in which the portion of thefirst metal layer 52 next to the first metal photoresist 54 is undercutfrom the opening. Optionally, a dry etch process can be used. If anadhesive layer 48 is used, then the adhesive layer 48 is preferably dryetched to form an isotropic profile having substantially parallel sidewalls from the first metal layer 52 to the substrate 10 surface. Theetching of the first metal layer 52 and the adhesive layer 48 createsthe emitter well 68.

[0051]FIG. 13 illustrates the result of a deposition of the tunnelinglayer 30 on the processed substrate 10. The tunneling layer 30 isapplied to and disposed on the surface of the first metal photomask 54and the exposed surface of substrate 10 within the emitter well 68.Preferably the tunneling layer 30 is applied to a thickness of about 50to about 100 Angstroms using a high dielectric film such as TiO_(x),WSiN, TaAlO_(x), AlO_(x), AlO_(x)N_(y), and TaAlO_(x)N_(y), butpreferably TiO_(x) to about 100 Angstroms. Other possible dielectricfilms include silicon-based dielectrics such as about 200 to about 500Angstroms of SiN and SiC. Other dielectrics that can be used to create ametal insulator semiconductor emitter are known to those skilled in theart.

[0052]FIG. 14 is an illustration of a lift off process used to removethe first metal photoresist 54 and the tunneling layer 30 that isdeposited on it. An oxygen rich ash etch is used to remove the firstmetal photoresist 54 and the portion of the tunneling layer 30 on thefirst metal photoresist 54. Preferably the process used is directionalenough to not affect the portion of tunneling layer 30 disposed in theemitter well 68.

[0053]FIGS. 15 and 16 are charts of temperature over time foralternative annealing processes 140 and 142, respectively, used toincrease the emitter current from the emitter. In FIG. 15 the processedsubstrate 10 after the ash etch in FIG. 14 is raised to a temperature of400 C. within about 10 minutes and held there for about 30 minutes.Then, the process substrate 10 is slowly brought back to roomtemperature (about 25 C.) over about 55 minutes. In FIG. 16, theprocessed substrate 10 is raised from room temperature to about 600 C inabout 10 minutes and held there for about 30 minutes. Then the processedsubstrate 10 is slowly brought back to room temperature over the courseof about 100 minutes.

[0054]FIG. 17 illustrates the application of polymer layer 56 onto thestack of thin-film layer 38 on the processed substrate 10. The polymerlayer 56 is preferably applied using a positive photoresist such asnovolac based resist although it is anticipated that SU8 material wouldwork. Preferably the resist is spin-coated to about 5.5 to about 6.5microns thick and baked on a contact hot plate at about 125 C. for 2min. The thickness of the polymer material is determined by the lensdesign and can range usually between about 2 microns and about 12microns. Because polymer material may have volatile components, thepreferred process is to perform a curing of the polymer material toremove most of the volatile content.

[0055]FIG. 18 is a chart of an exemplary curing process to remove thevolatile content from the polymer layer 56 material. The processedsubstrate 10 with the applied polymer layer 56 is placed in an over andthe temperature is ramped up from room temperature (about 25 C.) to 180C. in about 1 hour. Then the polymer is cured at 180 C. for about 4hours before the substrate is ramped down back to room temperature inabout 1 hour. The curing process is easily adjusted to account tooptimize for different polymer materials. Using this process with thenovolac based resist, empirical results show that a vacuum of 5×10⁻⁸Torr can be maintained using the polymer layer 56.

[0056]FIG. 19 illustrates the results of an application of a secondconductive layer 58 on the polymer layer 56 used as a lens layer. Theinterface between the second conductive layer 58 and polymer should havea low stress to provide a smooth surface and to prevent cracks andvoids. Empirical testing indicates that using gold, which is malleable,for the second conductive layer 58 provides such a low-stress interface.Other malleable conductive layers or metals and semiconductors that havea temperature expansion coefficient substantially similar to the polymermaterial chosen can be used as the second conductive layer 58. Thus, theactual selection of material for the second conductive layer isdependent on the choice of polymer material used to create the spacerbetween the emitter and the lens layer.

[0057]FIG. 20 illustrates the result of an etch of the second conductivelayer 58 to create a lens opening having a lens diameter 64. To performthe etch, a second conductive mask 62, preferably photoresist, isapplied to the surface of second conductive layer 58 and patterned toprovide an opening where the second conductive layer 58 is etched. Theopening is determined by the desired lens geometry but is preferablycentered over the emitter surface in the emitter well 68. The lensopening is also used to perform an etch of the polymer layer 56 therebyexposing the tunneling layer 30 on the substrate 10 surface.

[0058]FIG. 21 illustrates the result of the polymer layer 56 etch. Theetch is preferably done in DryTek 384T. Preferably the second conductivemask 62 is left on the second conductive layer 58 to prevent the secondconductive layer becoming partially etched during the polymer etchprocess. During the polymer etch, the O₂ level is about 200 sccms, thepressure about 2500 mT, the power set to about 85 Watts, the He pressureset to about 10 Torr and the top temperature to about 20 C. and thebottom temperature to about 12 C. The etch process takes about 135minutes to clear about 6.5 microns of resist. The etch recipe generatesabout 95 V of DC bias. The etch process balances the etch rate, etchresidue, and power to maintain as small a DC bias as possible. Thehigher the power, the faster the etch rate but more residue created. Thepower should be chosen to prevent the second conductive layer 58 fromsputtering, thus causing residue that is difficult to remove. Preferablythe resulting etch profile creates an undercut 61 that is about 1 toabout 2 microns for about each 6.5 microns of thickness of the polymerlayer 56 etched. By using a polymer etch process the etch selectivitybetween the polymer and the tunneling layer material, such as TiO_(x) ishighly selective, preferably greater than 1000:1. Empirical test resultsshow that the etch selectivity for the preferred process is about6000:1, meaning that the etch rate for polymer is about 6000Angstroms/min and the TiO_(x) is less than about 1 Angstrom/min.

[0059]FIG. 22 illustrates the application of a cathode layer 36 to thesurface of the tunneling layer 36, sidewalls of the emitter well 68, andthe surface of the second conductive layer 58 after the secondconductive mask 62 is removed. Preferably, the cathode layer 36 isdeposited to a thickness of about 50 to about 150 Angstroms of platinum,more preferably about 100 Angstroms. Other materials for the cathodelayer 36 include iridium, gold, and tungsten just to name a few, butpreferably platinum.

[0060] It should be noted that it would be obvious to those skilled inthe art that many variations and modifications may be made to thedisclosed embodiments without substantially departing from theinvention. All such variations and modifications are intended to beincluded herein within the scope of the present invention, as set forthin the following claims.

What is claimed is: 1-26. (cancelled).
 27. An electron lens for anelectron emitter, comprising: a focusing lens layer; and a polymerspacer layer between the focusing lens layer and the electron emitterwherein the polymer spacer layer defining at least one opening having anundercut of about 1 micron to about 2 microns per about 6.5 microns ofdepth.
 28. The electron lens of claim 27 wherein the polymer spacermaterial is between about 2 microns and about 12 microns thick.
 29. Theelectron lens of claim 27 wherein the polymer spacer layer has beencured to remove volatile content.
 30. A focused electron emittercomprising the electron lens of claim
 27. 31. An electronic devicecomprising at least one electron lens of claim
 27. 32. A focusedemitter, comprising: a tunneling layer less than about 500 angstroms inthickness disposed on a semiconductor substrate; a polymer spacer layerdisposed on the semiconductor substrate and defining a first opening,having an undercut of about 1 micron to about 2 microns per about 6.5microns of depth, disposed over the tunneling layer; a focusing lenslayer disposed on the polymer spacer layer and defining a second openingdisposed over the tunneling layer; and a cathode layer disposed on thetunneling layer.
 33. The focused emitter of claim 32 wherein the polymerspacer layer is between about 2 microns and about 12 microns thick. 34.The focused emitter of claim 32 wherein the polymer spacer layer hasbeen cured to remove volatile content.
 35. An electronic devicecomprising at least one focused emitter of claim
 32. 36. The electronicdevice of claim 35 wherein the electronic device is a display device.37. The electronic device of claim 35 wherein the electronic device is amass storage device.
 38. A focused electron emitter, comprising: atunneling layer less than about 500 angstroms in thickness; means forfocusing electrons emitted from tunneling layer; and polymer means forspacing the means for focusing electrons from the tunneling layerwherein the polymer means has been cured to remove volatile componentsand defines an opening having an undercut of about 1 micron to about 2microns per about 6.5 microns of depth.
 39. The focused electron emitterof claim 38 wherein the tunneling layer is about 100 Angstroms.
 40. Thefocused electron emitter of claim 38 wherein the means for focusingelectrons and the polymer means for spacing have substantially the sametemperature expansion coefficient.